The invention relates to a method of obtaining starch from grain or ground grain products by a wet process, wherein process water is added to the grain and the grain is first subjected to a steeping, the steeping is followed in some cases by a preliminary fragmentation for the purpose of then degerminating the product, the product is then subjected to an extensive fragmentation followed by the separation of fiber by means of sieves, and the separation of starch and suspended protein is performed by centrifugation.
Such methods of producing starch from grains are known, especially the production of starch from corn. The steeping of the corn is performed discontinuously in a counterflow apparatus with the addition of sulfur dioxide to the steep water, and after about 35 to 50 hours of steeping at a temperature of 45.degree. to 60.degree. C., an optimum disruption of the morphological structure between the elements of the grain as well as the starch grains and the protein is achieved, which is necessary in order to separate the starch grains from suspended protein and to refine the starch.
The fatty germ can be separated from the steeped corn after preliminary fragmentation by wet grinding, on the basis of the difference in density, before another fragmentation of the degermed product is performed, for example in a high-speed attrition mill, followed by the separation of hulls and fibers by sieves and the separation of starch grains and suspended protein by centrifugal separators.
The above-mentioned very complex and to some extent only empirically explainable steeping process has proven to be an indispensable step in the production of starch.
It is precisely in the steeping process that the difficulty is encountered in starch production. Furthermore, on account of the long steeping time that is required, very large batches of raw material are always involved in the process.
Disadvantages which the steeping process entails, such as the great investment and maintenance costs of the steeping apparatus, large floor space requirements, poor flexibility in the event of sudden changes in production requirements, as well as high consumption of energy and adjuvants have had to be accepted heretofore.
Furthermore, substances which go into solution, due to no small extent to microbial reactions which occur during the long steeping process, place an additional burden on the refinement of starch due to the addition of fresh water. Losses occur, for example, of dissolved proteins and carbohydrates which, after thickening in evaporators, are added to the hulls and fibers before drying. Also, substances contained in the grain are lost in the form of gaseous and steam-volatile metabolites due to microbial degradation.
The necessity of concentrating all of the steep water in order to recover dissolved and colloid substances also entails the great expense of evaporation and drying.
The condensate from the steep water evaporation cannot be recirculated on account of its high content of steam-volatile substances, and it constitutes a biological pollution problem in the sewerage.
The use of sulfur dioxide as an aid in the stabilization and control of fermentation during the lengthy steeping process has created the need for special precautions to safeguard personnel and equipment.
Heretofore it has been impossible to perform the costly steeping process continuously and shorten it while nevertheless permitting the desired separation of grain components.
In the article, "Biochemisch-technologische Studien uber die Nassverarbeitung von Mais" in the publication Starke 21 (1972), pp. 68-73, reference is made to Russian attempte to grind the grain coarsely, and then steep it in horizontal diffusers under ultraviolet irradiation or with the application of ultrasound in one instance, and to hull or coarsely grind the grain, for the purpose of shortening the steeping time; however, studies have shown that the starch yield is diminished by this method and the quality of the starch is poorer.
A method for the continuous steeping of starch has been disclosed in DE-AS No. 12 88 530, wherein a continuous steeping of corn combined with chemical treatment with sulfuric acid has been proposed. In the Additional Application DE-AS No 13 01 976, the method is improved by washing the steeped corn until the wash water has a neutral reaction. Then the corn is additionally steeped in hot water containing NaHCO.sub.3. The steeping time in this procedure is said to be reduced to 6 hours, and the steeping is said to be performed in a horizontally disposed pipe system.
Nothing is known about the biochemical and microbial processes involved in this steeping method. However, the increase of the dry matter content in the steep water to 8 percent indicates an appreciable leaching out of the corn grains.
The process was repeated on a laboratory scale, and it was found that it failed to achieve the quantities and qualities obtainable by the conventional sulfur dioxide counterflow process. It is probably for this reason that the process has not yet been adopted in practice.
All of the methods disclosed for reducing the cost of obtaining starch from grains or ground products of grain concentrate on the steeping process, which in any case results in a considerable exchange of substances. In addition to the absorption of water, it is always chemical or microbial reactions which form the basis for the cleavage of the starch-to-protein bond. In the known methods, mechanical action subsequent to the steeping is unimportant and serves only for the fragmentation of the grain structures.